1. Field of the Invention
The invention relates to an excess temperature protection element that is particularly suited for photovoltaic systems, but may also be used in other free wired electrical systems in interior and exterior areas.
2. Discussion of the Prior Art
In photovoltaic systems, an excess temperature protection element serves to electrically disconnect individual photovoltaic modules in hazardous situations. This excess temperature protection element also meets all electrical and safety technical requirements demanded of connector elements certified for operation in photovoltaic systems. The individual photovoltaic modules are usually series connected. At the end of the chain or string of modules, voltages of up to 1000 V DC voltage and currents of 8 to 16 A may occur when the sunlight is strong. Hazardous situations can arise, such as a fire on a roof structure on which a photovoltaic system is installed, or a collision of a motor vehicle with a PV system in an open field. Such situations pose an acute risk for emergency personnel or persons involved in the accident, should they come into contact with life-threatening levels of electric voltages or currents in the modules.
Currently, safety precautions for photovoltaic systems in the open field are limited to a requirement that they be enclosed by a fence. Thus far, there are no safety precautions for rooftop installations, because these are difficult to reach anyway.
Risk of injury to persons due to electric shock from photovoltaic systems, or in the worst case scenario, even death is rising, however, because of a steady increase in the number and size of photovoltaic systems. Thus, it is necessary to provide additional safety measures for the operation of photovoltaic systems.
The prior art provides few solutions that have the goal of reducing the risk of electric shock by photovoltaic systems, or which may at least be used for this purpose.
A safety device described in U.S. Pat. No. 4,380,001 A interrupts an electrical connection when a current or a temperature is exceeded. For this purpose a fusible wire element and a temperature-sensitive element are accommodated in separate chambers in a housing. Both elements are series connected. The temperature-sensitive element may be constructed either as a solder metal coated with pine resin or as a bimetal thermostat switch. When a critical temperature is exceeded, the solder melts and the thermostat switch opens.
Although the safety device is in principle able to open circuits, even in case of a temperature rise resulting from a fire, it is not possible to achieve a safe and permanent isolation of voltages of up to 1000 V with the fuse device or thermostat switch.
JP 11040838 A recommends switching a temperature safety unit into the outgoing line of photovoltaic modules with the goal of reducing the risk of electric shock for emergency or service personnel after a fire. The mode of operation of the temperature safety unit is not described in any detail. Because of the high voltages that may occur, the isolating distance would have to be relatively large, to avoid any sparking or arc-overs when separating the photovoltaic systems. Nowhere in the publication, however, is there a discussion of how such an isolation distance may be achieved in the temperature safety unit. Furthermore, both safety devices mentioned above have the disadvantage that they cannot be activated by a blow or an impact applied by emergency staff, as is often necessary in rescue missions.
DE 10 2008 027 189 A1 introduces an excess temperature protection element for photovoltaic systems that isolates individual photovoltaic modules from each other in situations of danger. The excess temperature protection element comprises a two-part safety body in which a disconnectible electric connecting element comprising a connector pin and socket, as well as a pre-stressed pressure spring, are arranged. Preferably, the two parts of the safety body have an opening on one side, wherein the opening of one part is expanded, and the other part is plugged into the expanded opening on the open side thereof. The exterior wall of the plugged in part is soldered onto the interior wall of the expanded part, to prevent the pressure spring from pushing the two components apart.
The excess temperature protection element safely isolates the photovoltaic modules from each other during a fire, but it is not possible to mechanically deactivate the modules. The solder joint connecting the two parts of the safety body is, however, subjected to environmental influences, such as temperature fluctuations, moisture, and UV radiation, in addition to the high, continuous forces caused by the spring, and, as a result, the solder joint often dissolves after only several months, leading to an uncontrolled and undesired shut-down of the photovoltaic modules.
What is needed, therefore, is a excess temperature protection element that eliminates the disadvantages of the prior art.